Verhandlungen der Deutschen Physikalischen Gesellschaft (Deliberations of the German Physical Society)", (a):Vol. 17, Number 22, p.407-418 / (b):Vol. 17, Number 22, p.418-419 / (c):Vol. 17, Number 24, p.438-451, 1915
Sitzungsberichte der K\"oniglich Preussischen Akademie der Wissenschaften (Reports of the meetings of the Royal Prussian Academy of Sciences) Vol.31, p.653-667, 1916